The present invention relates to a human-body protective, cushioning helmet interface (shock-absorbing) structure (cushioning pad) which is designed especially to be employed as part of a plural-pad distribution deployed within a rigid protective helmet-shell barrier structure to protect the head from a blunt-trauma-type impact injury. More particularly, and from a broadly stated point of view, it relates to a site-selectable, helmet-installable load-cushioning pad taking the form of compressible viscoelastic foam componentry with a structure possessing a load-response behavior which (a) resists sudden-movement rapid compression, yet (b) is less resistive to slow-movement compression.
From a methodologic point of view, the invention features the steps of (a) providing a compressible, viscoelastic load-cushioning pad body for installation inside a helmet, and (b) pre-arming that pad body with load-response characteristics whereby, with the pad in place inside a helmet, the pad body responds to a motion load with behavior which (1) resists sudden-movement, rapid compression, yet (2) offers less resistance to slow-movement compression.
As will be seen, there are other special features and steps which further characterize this invention.
While there are many helmet applications wherein the structure and methodology of the present invention can offer distinct advantages, one preferred embodiment of, and manner of practicing, the invention are described herein specifically in the setting of a military helmet with respect to which the invention has been found to furnish particular utility.
With reference to a conventional military helmet, such an environment is vividly demonstrative of the issues that are successfully addressed by the present invention. For example, the current U.S.-issue military infantry helmet utilizes in its outer shell an internal webbing system combined with a removable leather liner to suspend the helmet on the wearer's head. Airspace between the webbing and the shell of the helmet contributes somewhat to the ballistic, and significantly to the cooling, capabilities of the helmet, but such a webbing system has proven consistently (a) to do a poor job of cushioning shock loads delivered to the wearer's head through the subject helmet, and (b) to be quite uncomfortable, and thus to be the source of many complaints from users.
The structure and methodology of the present invention offer appreciable improvements in these areas of concern regarding helmet performance. This structure and methodology of the invention described herein, feature a novel cushioning structure, and its performance, which offer the very important cooperative characteristics of compression-deformation-and-slow-return viscoelasticity, non-springiness, and what is known as acceleration-rate(strain-rate)-sensitivity. Another way of expressing these special qualities of the present invention is, as suggested above, to say that the invention features the use of compressible viscoelastic foam componentry (a pad) which resists sudden-movement rapid compression, yet which is less resistive to slow-movement compression.
According to the invention, it features a load-cushioning instrumentality formed from one, or a plurality of, body(ies) of a viscoelastic foam material which responds acceleration(strain)-rate-resistantly to shock-produced, sudden-motion, rapid acceleration, with this material having a resistance to resulting compression deformation that generally rises in a somewhat direct relationship to the level, or magnitude, of acceleration. Thus, the smaller (slower) the acceleration, the less resistant such material is to compression, and, the larger (faster) the acceleration, the more resistant it is to compression. This kind of acceleration-rate(strain-rate)-sensitivity is somewhat analogous to the phenomenon known in the world of fluid mechanics as shear-resistant fluid dilatancy. This behavior, in the “world” of a helmet shell, causes a shock load to be transmitted to, and borne by, the wearer's head over a relatively wide surface area, and thus generally reduces the likelihood of serious injury.
The rate-sensitive material proposed by the structure of this invention to form the core of a load-cushioning pad structure also responds to (and following) an impact event by recovering slowly from compression deformation to an undeformed condition—thus avoiding any dangerous “rebound”, spring-back activity. In point of fact, the load-cushioning material employed in accordance with the invention is decidedly non-springy in character. As will be further mentioned, the load-cushioning material proposed by the invention, in order to be capable of dealing most effectively in direct combination with a rigid helmet shell in the protection against head impacts, possesses a durometer with a minimum ILD number of about 15-ILD. In the environment of a helmet, the load-cushioning material used by the invention provides the only cushioning response acting between a helmet shell and a wearer's head.
The rate-sensitive core structure can be, selectively, either of a single-component or of a plural-component (plural sublayers) nature, and in the setting of a military helmet, preferably takes the form of two, individual, viscoelastic sublayers which have two different durometers. In this helmet setting, and during use by a wearer, the lower-durometer sublayer is employed closer to the head, and the higher-durometer sublayer is on the opposite side of the lower-durometer sublayer relative to the head, and is interposed the lower-durometer sublayer and the inside of a helmet shell. Within, and throughout the full, three-dimensional boundaries of each rate-sensitive, viscoelastic layer, the layer material therein is unfettered in its uniform, omnidirectional performance in response to introduced impact/shock loads. No other structure extends as a “non-homogeneous” anomaly through and in this region, which other structure would alter such uniform, all-over, load-response behavior.
The core structure may be encapsulated by a thin moisture barrier jacket.
The association which exists, according to the present invention, between the load-cushioning pad structure and a helmet shell, is that the helmet shell converts whatever kind of specific impact occurs to it from the outside to a broad-area, blunt-trauma kind of event which is delivered directly to the load-cushioning pad structure without there being any interposed, other load-managing material, such as any material with springy rebound (resilience) behavior. Such a blunt-trauma event presented through the shell to the load-cushioning structure takes maximum advantage of the cushioning capabilities of the load-cushioning structure, and results in significant anti-injury impact delivery to the head of a helmet wearer.
With the load-cushioning (shock-absorbing) structure of this invention incorporated for use in conjunction with an operatively associated helmet shell, a load-transmission path exists between that shell and the head of a wearer. In this path, compression deformation and return response to a shock load delivered to the outside of the shell is solely determined by the characteristics of the invention's load-cushioning pad structure. Nothing in this path introduces any form of a resilient, spring-back rebound response.
The structure of this invention is easily rendered in a variety of specific configurations, and thus is readily usable in a host of different helmet settings. It is relatively easy and inexpensive to manufacture, and it can be introduced very conveniently in a wide range of helmet “retrofit” situations. It is employed within, and in conjunction with, a helmet shell as a user site-selectable distribution of plural load-cushioning pads. Overall structure thickness can be selectively chosen to be different for different circumstances. A single, or more than two, rate-sensitive sublayer(s) can be employed in the core pad structure. Within a relatively wide range (set forth below herein), a different specific durometer value (or values in a stack of sublayers) for the rate-sensitive sublayer(s) can be chosen.
All of the special features and advantages mentioned above that are offered by the present invention will now become more fully apparent as the description which follows below is read in conjunction with the accompanying drawings.